I'm considering getting hold of this lens as a replacement for the kit 18-55 and as a first foray into L glass.

Reading reviews, a couple of things bother me slightly - the barrel distortion at 24mm, evident through to 50mm, and the other is the widespread comments of "this lens is pointless for crop-frame bodies".

Is the barrel distortion really that bad? Is constant correction with DxO necessary?

I've never quite understood the point of converting the focal lengths to the 35mm equivalent. The argument made by the reviewers are that on crop frame, 24mm is 38mm equivalent which isn't wide-angle - but it is on FF. But I say the kit lens is 18mm and we still apply a crop factor to that, making it 29mm. In any case, the starting point is only 2mm from my Sigma 10-20 UWA lens.

yeah but starting point of 28 is a huge difference to 38.
Put you kit lens on 24 and compare it to 18 to see difference.
I see you already have a wide angle Sigma.

If you need weathersealing ( is you body weathersealed ? ) and you need that length of zoom, its a good buy, especially if you go full frame in the future. Its a good lens for outdoor wildlife photography where the 70-300 or 100-400 can be too long.

For a general purpose lens for a crop sensor there is the 15-85, 17-55 or for something cheaper the tamron 17-50 non vc.

The 17-50 or 55 at 2.8 is useful if you specialise in portrait or low light, but possibly a prime may serve you more.

Keep thinking that a L zoom in the 70-200 or 300 or 100-400 maybe more use, especially that the 24-105 is not a perfect lens and F4 isn`t that exiting either on a cropped body.

Hi maxjj, yeah I've got a number of lenses, I'm just plotting a path to getting my hands on a 5D2 as I'm quite into landscape work. EF-S lenses, whilst excellent are not something I want to spend my money on. The general consensus with L glass is that you'll notice the difference optically with contrast and thank yourself for the handling benefits, waterproofing, resale value etc.

My body's a 500D, which I've certainly not outgrown. I've got the 50/1.8 and the new Tamron 70-300 VC, plus the kit lens. I do have in my sights the 70-200/4 IS USM at some point, I believe it's sharper than the 2.8.

The 24-105 caught my attention because of it's reasonable used-market cost, the 3-stops effective IS and constant aperture (bear in mind my UWA and telephoto begin at F4, so I'm not interested in the cost penalty of the 24-70 F2.8 ). It's also a better bet than the 17-40L at this point, as a 5D2 will see the bottom end of the 24-105 as crop frame 15mm, nice and wide until I find a 17-40 at reasonable cost. The 17-40L doesn't have IS, nor is it's zoom range sufficient to be a practical walkaround lens.

I've still got my UWA Sigma, so if I bought this lens, I'd be missing the 4mm between the Sigma finishing at 20 and this starting at 24. I'll still have "zoom with my feet" though!

Please pick holes in my argument, it'll help me get the right lens in the end!

lol, I am picking holes in my own arguments too. I often find that I am chasing birds or wildlife and I could benefit from a weathersealed lens wider than 70, ( sometimes the 70-300 isn`t wide enough) the 24-105L would fit that spot nicely. Not really into landscape photography.

But what I need is a bit more subject isolation, f4 is sufficient for my needs from around 80 on and the 70-300L is really nice for that. I worked out that the 70-300 is a bit like a 70-200 f4. Except is has more reach and better is. I don`t need f4 at 200, there is enough dof on the 70-300L
If the 17-55 is usm was weathersealed, I would already have it. As it is not I cannot commit to it. I find it hard to scrape up the cash on the big 24-70L though, but I might end up doing that.

I can keep going around in circles

The ideal lens for me would be a weather sealed 30-130 2.8L IS USM for a cropped body.
Will I go FF?
Unlikely, in the near future, as the price of the new 5D III will be too high and the old one lacks things I want; stuff that I currently have in the 7D.